I do not see why do you need to use AWS load balancer or change Alfresco SSL certificates.

The simplest aprox is to configure an apache httpd (or nginx) virtual host in 443 and to use letsencrypt certbot for getting the certificates of your public machine. In the virtualhost, you should proxy /alfresco and /share to the tomcat ports (via http or ajp). You do not need to touch Alfresco config for this, a usual aprox is to secure only the frontend. You may disable 8080 connector and do proxypass via ajp to 8009 port too.